3.4.6 - Indirect contact
protection
There are three methods of providing protection
from shock after contact with a conductor which would not
normally be live:
1.
- making sure that when a fault occurs and makes
the parts live, it results in the supply being cut off within
a safe time. In practice, this involves limitation of earth
fault loop impedance, a subject dealt with in greater detail
in {5.3}.
2.
- cutting off the supply before a fatal shock can
be received using a residual current device {5.9}.
3.
- applying local supplementary equipotential bonding
which will ensure that the resistance between parts which
can be touched simultaneously is so low that it is impossible
for a dangerous potential difference to exist between them.
It is important to stress that whilst this course of action
will eliminate the danger of indirect contact, it will still
be necessary to provide disconnection of the supply to guard
against other faults, such as overheating.
It is important to appreciate that in some
cases a dangerous voltage may be maintained if an un-interruptible
power supply (UPS) or a standby generator with automatic
starting is in use.
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